impurity transport at jet on-going analysis from recent campaign

Carine Giroud 1 ITPA Naka 1.10.2007

Impurity transport at JETOn-going analysis from recent

campaign

C. Giroud, C. Angioni, L. Carraro, P. Belo, I. Coffey, V. Naulin, M-E. Puiatti,

M. Brix, H. Leggate, K. Lawson, A.D. Whiteford, M. Valisa.


• Linear relationship assumed between impurity flux and density gradient

Experimental determination of transport coefficients

zzzz VnDΓ

r

nz

Diffusion coefficient

Convection coefficient

Vz >0 outwards

• Extrinsic impurities injected by laser ablation (Ni) or gas injection (Ne, Ar).

− D and V determined individually by modelling of time evolution of spectroscopic data

− Ni: soft x-ray and VUV − Ne and Ar: soft x-ray and VUV and also from charge exchange spectroscopy


NCLASS: neoclassical coefficients calculated from NCLASS

Time trace


Discharges analysed so far

A wide dataset of He, Ne, Ar, Ni has been collected: He still on-going analysis. many discharges cannot be analysed due to MHD, changing plasma conditions


• Global density peaking used in this talk:

– determined Vz and Dz

– assume a constant source nz(r)

– definition global impurity density peaking:

– also calculated corresponding peaking:

with Dmeas, V=Vneo

– for C, direct measurement of nz(r)

z

z

n

rn )0(

Volume

averaged

Measured peaking of impurity


– Z dependence

– For Argon, assumption V=Vneo with D=Dmeas does not reproduce peaking.

– Variation in Argon peaking

More discharges to be analysed.

Impurity peaking

Discharges without RF

ne /<ne>0.8 1.0 1.2 1.4

1.0

0.0

0.5

1.5

2.0

Closed symbol: [Dmeas, Vmeas]Open symbol: [Dmeas, Vneo]

0


Diffusion coefficients

ne /<ne>0.8 1.0 1.2 1.4

0

0.001

0.010

0.100

1.000

10.00

ne /<ne>0.8 1.0 1.2 1.4

0

0.001

0.010

0.100

1.000

10.00r/a~0.15 r/a~0.6


Transport coefficients: V

Z

V_ar measured different from neoclassical.

r/a~0.15

-4.0

-2.0

0.0

2.0

ne /<ne>0.8 1.0 1.2 1.4

0

r/a~0.6

C

Ne

Ar

Ni


Comparison L-mode and H-mode


Comparison H-mode and Hybrid

Ip/B

Ptot

Wdia

ne

Halpha

Peaking varies for Argon: MHD ?

Hybrid: black

H-mode color (-15.5s)


– Rf effect confirmed but local effect r/a~0.3

– Seem to be dependent on Z !

– Compatible with a neoclassical effect

Effect of ICRH

preliminary

Carraro EPS 2007

Giroud EPS 2007

Belo


Conclusion

• Work on-going on the analysis of impurity transport experiments from 2006-2007 database.Validation of consistent analysis technique and error analysis.

• First results:• L-mode/H-mode : similar peaking• Hybrid/H-mode: same peaking from C to Ar.• ICRH effect: core effect and maybe due to neoclassical effect.

• Ni transport analysis to be extended and He transport analysis started.

• Beta scaling and eff scaling

• Systematic comparison with theoretical models.


Two very different Ni profiles

ICRH dominant ionPeaked Ni profile

ICRH dominant electronSlightly hollow Ni profile

[M-E. Puiatti PoP 13 2006]

Steady-state profile


Recent development in turbulent transport theory

• Two main electrostatic micro-instability considered ITG/TEM

Microinstability ITG TEM

Direction of propagation

Ion diamagnetic

Electron diamagnetic

drive R/LTi R/LTe & R/Ln


Recent development in turbulent transport theory

• Three main mechanisms have been identified

Curvature pinch1 Compressibility of ExB drift velocity

Thermodiffusion pinch2

Compression of the diamagnetic drift velocity

Pinch connected to the parallel dynamics of the impurity3

Parallel compression of parallel velocity fluctuations produced along the field line by the fluctuating electrostatic potential

Decreases with increasing q

q

q

z

z

T

T

2[X. Garbet PoP 12 2005]2,3[C. Angioni C PRL. 96 2006]

1[J. Weiland NF 29 1989]1[X. Garbet PRL 91 2003]1[M. B. Isichenko PRL 1996]

1[D.R. Baker PoP 5 1998]1[V. Naulin Phys Rev. E 2005]2[M. Frojdh NF 32 1992]


Pinch mechanisms in theory of turbulent impurity transport

All contribute to the total turbulent pinch


Illustration of complex Z dependence of turbulent transport

• D and V calculated with the linear version of the gyrokinetic code GS2: only the fastest growing mode is taken in the quasi – linear model, no neoclassical transport included. Trace impurity considered.

• No general trend in Z of turbulent transport

specific calculation needed for studied discharge

GS2 [R/LTi=7, R/LTe=6, Te/Ti=0.88]

[C. Angioni]


ICRH dominant ionPeaked Ni profile

ICRH dominant electronSlightly hollow Ni profile

[M-E. Puiatti PoP 13 2006]

Steady-state profile

R/Ln=3.9R/LTe=4

Te/Ti=0.95R/LTi=6.6

R/Ln=5.2R/LTe=6.Te/Ti=1.

R/LTi=6.6

Different dominant instability for peaked and flat Ni density

ITG dominated TEM dominated

GS2


Measured Z dependence of impurity peaking

#66134

Neoclassic

measure-ment

measure-ment

Neoclassic

r/a =0.15

r/a =0.55

Negative C peaking

Peaking lower than neoclassical

stronger z dependence in core than at mid-radius

•Ne, Ar and Ni injected in ELMy H-modeq0>1, 0.1 <neff <0.2Bt=2.9T, q95=7, 2MW ICRH, 8.6MW NBI


GS2

Anomalous part:-R(V-Vneo)/(D-Dneo)

GS2 w/o Thermodiffusion

Neoclassic

#66134

Linear GK calculation reproduces trend of measured Z dependence

Discharge ITG dominatedR/LTi~5.8, R/LTe~6.3, R/Ln~0.3 and Te/Ti~1.1, *~0.10

GS2

Measurement


Discharges analysed so far

A wide dataset of He, Ne, Ar, Ni has been collected: He still on-going analysis. many discharges cannot be analysed due to MHD, changing plasma conditions

Ti/Te

impurity transport at jet on-going analysis from recent campaign

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